Histidine complexes with some bivalent cations

Abstract

Stability constants have been determined potentiometrically at 37° and I= 0·15 (KNO₃) for complexes present in aqueous solutions of histidine and bivalent ions of cobalt, copper, lead, manganese, nickel, and zinc. Except for lead, which gives only PbL⁺(where L^– is the histidine anion), all of these metals form complexes of the types ML⁺ and ML₂. In histidine–copper mixtures the protonated species Cu(HL)²⁺ and LCu(HL)⁺, and the hydrolysed species LCuOH and L₂Cu₂(OH)₂ are important. Zinc, and perhaps manganese, can also form M(HL)²⁺.